Regarding to variation of size of TiO[subscript 2] powder (400 nm and 1 m), reaction temperature (90-180 degree celsius ), and sonication power (0-38 W), morphology, length and phase of titanate nanostructures could be controlled. Transmission electron microscope (TEM), nitrogen adsorption (BET), dynamic light scattering (DLS) and X-ray diffractometer (XRD) have been employed to analyze structure, specific surface area, average size and crystalline phase of the synthesized products. For the effect of raw TiO[subscript 2] size, the smaller powder was transformed to titanate nanostructures with higher specific surface area than those of larger raw TiO[subscript 2] powder. Morphology of titanate product transformed from TiO[subscript 2] spherical particle to titanate nanosheet, nanotube and nanofiber with the gradual increase in the reaction temperature. The dependence of specific surface areas of titanate nanostructures on reaction temperatures are as follow: 150 > 120 > 90 > 180 degree celsius. Based on the effect of sonication power, the length and BET surfacte area of titanate nanotube (TNT) becomes longer and larger, respectively, with the applying sonication pretreatment. Furthermore, at 150 degree celsius, much longer TNTs with average hydrodynamic size of 490-1760 nm were produced when the sonication power was increased and the reported nanotube formation phenomena during the hydrothermal process, that is a mechanism contributing to length control is proposed. The interesting brookite phase was obtained after applying sonication pretreatment to synthesized titanate nanofiber. The photocatalytic activity of titanate nanostructures synthesized by hydrothermal process at the reaction temperature of 90 degree celsius to 150 degree celsius was investigated by degradation of phenol solution in comparison with that of titania raw powder. With an increase in the hydrothermal reaction temperature (90-150 degree celsius), the specific surface area of titanate nanostructures became higher (83-258 m[superscript 2]g[superscript -1]) and band gap energy (by UV/vis spectrometer) of titanate nanostructures also increased at 90-120 degree celsius (3.44-3.84 eV) and slightly changed at 150 degree celsius (3.81 eV). Meanwhile, their phase changed from anatase to titanate compounds. Interestingly, the synthesized titanate exhibits high UV adsorption capability but no intrinsic photocatalytic activity for phenol degradation.